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08 ML350 high temperature

2K views 10 replies 3 participants last post by  zft325 
#1 ·
Hi folks. I tried searching but can't find any solution

I have a 2008 ML350 4matic gas. It's got 170k miles. The car drives fine except for a high temperature problem that a couple local shops can't diagnose.

I first noticed the problem when I hear my engine fan going to max all the time. People on the street would be looking at my car to see what making the noise. Since I live in SoCal, it's hot here all the time, so I thought nothing of it at first. Then the fan would hit max even driving at night when it's 60 outside. Just regular driving. No revving high rpm, no racing Porsches.

This past heatwave, while driving on surface streets, I noticed the engine is a lil low on power, and the Ac is cutting off, so I checked the temp, it hit 125+. But quickly lowered to below 100 within 20 seconds of changing lanes trying to pull over. The temperature has been around 90-110 regularly.

Oh, I usually get 400miles out of a tank of gas, but only averaging 370 nowadays. Went to two shops, they checked and test the car for couple days and found nothing. Suggested that I try the stealership.

Got any ideas?

Thanks.
 
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#3 ·
Thanks for the quick response!

My preschool kids are with me pretty much all the time, in the socal heat, my ac is on 100% during the day. So I guess it's on when it happens. If it's not too much trouble, do you mind explaining to me why would high ac pressure cause higher engine temperature? what causes high ac pressure? what can I do about it? or does it have to go to a shop?

Thanks!
 
#4 ·
when you say high temp can you see wheres your actual temp on the dash? when freon is on the high side it can cause heat on your ac condenser. that explains the ac cut off during high temp. thats to protect the system from overheating. but it can also be vice versa, when the engine overheats it will cut off your ac aswell.
 
#5 ·
I've been switching the display to the temperature bar after hearing the fan being on max all the time. Seems the fan kicks on max when the temp reaches 96~97ish. The temperature would raise over 100 once in a while in traffic. and of course that time when it went above 125.

But temp always drops down very fast, just not low enough to slow down the fan from max speed.

Picture me driving through a very quiet residential area at 11pm (when I get off work) with my fan on max. My kids can hear me 1 block away and always wait for me with the garage door open by the time I arrive....
 
#6 ·
here are things to check: 1. thermostat valve, 2. radiator row blockage. 3. fan. start with the thermostat valve located inside the hose. with the miles you have it might be due for replacement. be carefull on driving at 125 heat. can warp and damage alot of things with that temp.
 
#7 ·
Hmm, Just because it's 7 years old, I'd replace the thermostat and drain and fill the coolant. It's getting hot, which is either the thermostat not controling temp, the water pump not pumping, or the radiator clogged not allowing good cooling.

If you have a infrared thermometer you can check and see what the temperature actually is. They are $25 at harbor freight and useful to see what's going on. Check temp in and out of the radiator, the housing of the thermostat and the return line into the overflow tank. You can just feel the return line to see if it's hot, that gives you a clue that the water pump is pumping.

I had a W202 that had a temp sensor go bad, though it was overheating but the car was fine, just the indication. The temp sender will cut off the AC and make the engine management act wonky too.
 
#8 ·
You guys are great!

I was thinking thermostat too. Perhaps it's not working properly. I mentioned this to both shops, and they both said that since they can't confirm it's the thermostat, and the car is still working in OK temp most of the time, they didn't want to unnecessarily change it and have it not solve the problem. I'll pick up a infrared thermometer tomorrow and see if the car's reading the temps right.
 
#9 ·
the most easiest way to check is try to hold the hose from the top and bottom. when in the normal temp it should both be hot. if one is cold then you have a stuck thermostat. i did this on my bmw and found it very helpful
 
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